The air flow control valves used automotive air conditioning and ventilation systems (typically abbreviated as “HVAC systems”) generally have a large, generally box shaped plenum or housing containing an evaporator (cold air source), heater core (hot air source) and several air directing and handling mechanisms that determine the mix of hot and cold air streams, so as to achieve a desired temperature, and also the ultimate exit point of tempered air within the vehicle interior, generally referred to as mode control.
A typical HVAC system is illustrated in FIG. 1. Box shaped housing 10 contains an evaporator 12 and heater core 14, arranged so that forced air (from a non illustrated blower) all flows through evaporator 12, and then through heater core 14 (or not) in a proportion determined by the relative position of a swinging door type temperature valve 16. As illustrated, temperature door 16 is in a mid position, so that a stream of both hot and cold air travel upwardly to a common area above which are located several potential exit ports into the vehicle interior. Typically, these comprise an uppermost defroster outlet 18, a midlevel air outlet 20, and lowermost, floor directed, heater outlet 22. These various outlets are best distinguished by their location, rather than the temperature of the air that is directed to them, since that air may have any temperature, achieved by mixing the two air streams. Achieving a thorough air mix has been a continuing problem, however, because of a tendency for the distinct cold and hot air streams to remain stratified.
Another continuing problem has been providing for mode control, that is, the selective opening and closing of the three possible air outlets, in a fashion that is effective in terms of sealing efficiency, occupied space, and cost. The most common opening and closing mechanisms found in production are flapper door type valves, as illustrated in FIG. 1 at 24, 26 and 28, respectively. Such doors are pivoted back and forth by individual motor and gear drives, which act about an axle at the rear edge of the doors. As such the sealing force applied at the remote outer edge of the doors is potentially compromised. An analogy would be closing a book by pinching the covers together at a point near the spine. The closing force would be strongest near the spine, but questionable at the outer edges of the pages. The flapper door closing force issue is also affected by the common practice of using a layer of foam on the door, which must be compressed against the lip of the opening by the closing force applied to the door.
Many alternatives to flapper door valves have been proposed. Among these are continuous belts, so called film valves, in which a belt of flexible material is rolled back and forth in order to cover and uncover vent] openings. Film valves are effective, but costly, and can require a substantial redesign of the housing or module to accommodate them. Other proposals have included rotating barrels, butterfly valves, arcuate sliding doors, and articulated, “roll top desk” type panels. One distinctive design, disclosed in U.S. Pat. No. 5,228,475 is a swinging panel that pulls flat against the lip of an opening, and thereby provides even, strong sealing force. However, it swings up and down between two adjacent openings, rather than covering and uncovering a single opening to a greater or lesser extent. All of the aforementioned proposals are generally not capable of being simply substituted for flapper type doors to open and close individual vent openings, with little or no change to the layout of the housing itself.